As a fluid machine forming a part of a refrigeration cycle apparatus, an expander-compressor unit 400 is known that is constituted by integrating a compression mechanism 402 for compressing a refrigerant with an expansion mechanism 404 for allowing a refrigerant to expand and converting into mechanical energy the expansion energy generated during the refrigerant is expanded and decompressed, as shown in FIG. 6 (see JP 62(1987)-77562 A). In the expander-compressor unit 400, the mechanical energy resulted from the conversion by the expansion mechanism 404 is utilized as a part of energy for rotating a shaft 405 of the compression mechanism 402. This reduces input to the compression mechanism 402 from outside, and improves the efficiency of the refrigeration cycle apparatus.
Since the compression mechanism 402 adiabatically compresses the refrigerant, a temperature of the refrigerant rises in the compression mechanism 402. Accordingly, temperatures of components of the compression mechanism 402 also rise in accordance with the rising temperature of the refrigerant. On the other hand, the expansion mechanism 404 draws the refrigerant cooled by a radiator, which is not shown, and allows the drawn refrigerant to expand adiabatically. Accordingly, the temperature of the refrigerant lowers in the expansion mechanism 404. As a result, temperatures of components of the expansion mechanism 404 lower in accordance with the lowering temperature of the refrigerant. Thus, mere integration of the compression mechanism 402 and the expansion mechanism 404 as described in JP 62(1987)-77562 A allows the heat of the compression mechanism 402 to transfer to the expansion mechanism 404, which heats the expansion mechanism 404 and cools the compression mechanism 402. In this case, in an actual cycle, enthalpy of the refrigerant discharged from the compression mechanism 402 decreases (see Point B→Point B1) and heating capacity of the radiator deteriorates to be lower than in a theoretical cycle, as shown in the Mollier diagram of FIG. 7. Moreover, enthalpy of the refrigerant discharged from the expansion mechanism 404 increases (see Point D→Point D1), and refrigerating capacity of an evaporator deteriorates. The deteriorations in the capacities of the radiator and the evaporator are not preferable because they mean a decrease in the efficiency of the refrigeration cycle apparatus.
Particularly, when the refrigeration cycle apparatus is used as a water heater, it needs to heat water by its radiator to a temperature predetermined for hot reserve water. Accordingly, the refrigerant used for heating, that is, the discharge refrigerant from the compression mechanism 402, must have a temperature higher than the predetermined temperature for reserved hot water. However, when a thermal short occurs between the compression mechanism 402 and the expansion mechanism 404, the temperature of the discharge refrigerant from the compression mechanism 402 lowers, and accordingly, the temperature of the reserved hot water lowers. There is a method of increasing a pressure of the discharge refrigerant from the compression mechanism 402 in order to compensate the temperature of the discharge refrigerant from the compression mechanism 402 lowered by the thermal short. In the Mollier diagram of FIG. 8, Point A→Point B2→Point C2→Point D2 shows a theoretical cycle of discharge temperature control, and Point A→Point B3→Point C2→Point D3 shows an actual cycle of discharge temperature control. As seen, when the refrigerant is compressed somewhat excessively, the temperature of the discharge refrigerant can be raised, and thereby the temperature of the discharge refrigerant substantially can be maintained at the target temperature. However, this method makes the compression mechanism 402 perform excessive work, increasing the power consumption at a motor. Therefore, the effect in recovering mechanical power by the expansion mechanism 404 is reduced.
In order to solve such a problem, a configuration is known in which a heat insulating material 504 is provided between a compression mechanism 501 and a expansion mechanism 502 as shown in FIG. 9 (see JP 2001-165040 A). Reference numeral 503 indicates a shaft coupled to the compression mechanism 501 and the expansion mechanism 502. Since the heat insulating material 504 is sandwiched between the compression mechanism 501 and the expansion mechanism 502 in the configuration shown in FIG. 9, heat transfer between the compression mechanism 501 and the expansion mechanism 502 can be reduced. However, such a configuration increases the cost for the heat insulating material 504.
On the other hand, an expander-compressor unit also is known that reduces the heat transfer between the compression mechanism and the expansion mechanism without the heat insulating material (see JP 2005-264829 A). JP 2005-264829 A discloses a configuration in which a compression mechanism 602 and an expansion mechanism 604 are disposed spaced apart, and an interior of a closed casing 601 is filled with a low pressure refrigerant guided from an evaporator to the compression mechanism 602, as shown in FIG. 10.
A configuration also is known in which an interior of a closed casing 701 is partitioned into a low pressure side space 752 and a high pressure side space 751, an expansion mechanism 702 is provided in the low pressure side space 752 while a compression mechanism 704 is provided in the high pressure side space 751, as shown in FIG. 11 (see JP 2006-105564 A). In the expander-compressor unit of FIG. 11, the suction refrigerant that will be drawn into the compression mechanism 704 is guided to the low pressure side space 752, and the refrigerant that has been discharged from the compression mechanism 704 is guided to the high pressure side space 751.
In the configuration shown in FIG. 10, the compression mechanism 602 and the expansion mechanism 604 are separated from each other, and thereby heat transfer between the compression mechanism 602 and the expansion mechanism 604 can be reduced. A surrounding space of the expansion mechanism 604 is filled with a relatively low temperature refrigerant that will be drawn into the compression mechanism 602. This makes it possible to suppress an increase in enthalpy of the refrigerant discharged from the expansion mechanism 604. Although the heat transfer occurs also between the compression mechanism 602 and the suction refrigerant, the refrigerant that has received heat from the compression mechanism 602 is compressed by the compression mechanism 602, and heats the compression mechanism 602. Therefore, the discharge temperature of the compression mechanism 602 does not lower. As a result, a decrease in enthalpy of the refrigerant discharged from the compression mechanism 602 is suppressed.
However, in the configuration in which the interior of the closed casing 601 is filled with the low pressure refrigerant as described above, the discharge refrigerant from the compression mechanism 602 is discharged directly out of the closed casing 601 via a discharge pipe 609. Thus, an amount of the oil discharged out of the closed casing 601 is larger in this configuration than in the configuration in which the interior of the closed casing 601 is filled with the discharge refrigerant from the compression mechanism 602. The discharged oil adheres to a refrigerant pipe and increases pressure loss of the refrigerant, as well as deteriorates the capacities of the radiator and the evaporator, exerting an adverse effect on the performance of the refrigeration cycle apparatus.
On the other hand, in the configuration shown in FIG. 11, the discharge refrigerant from the compression mechanism 704 is once released into the high pressure side space 751 of the closed casing 701, and then is discharged from the closed casing 701 toward the radiator via a discharge pipe 709. Since the discharge refrigerant is once released into the high pressure side space 751 in this way, the oil is separated easily from the discharge refrigerant from the compression mechanism 704 in the closed casing 701. Thus, the discharge refrigerant from the compression mechanism 704 does not circulate in the refrigeration cycle apparatus together with a lot of oil
However, since the interior of the closed casing 701 is partitioned into the low pressure side space 752 and the high pressure side space 751, a shaft 705 coupling the expansion mechanism 702 to the compression mechanism 704 needs to penetrate through a partition 750. Such a configuration absolutely requires a mechanical seal for preventing the refrigerant from leaking through a clearance between the shaft 705 and the partition 750. There arises a concern that the sliding loss may be increased between the shaft 705 and the mechanical seal.
As the layout of the compression mechanism, the expansion mechanism, and the motor in such an expander-compressor unit, JP 2003-139059 A proposes four kinds of layouts shown in FIG. 12A to FIG. 12D. In FIG. 12A to FIG. 12D, C indicates the compression mechanism, M indicates the motor, E indicates the expansion mechanism, and P indicates an oil pump. However, JP 2003-139059 A does not disclose detailed configuration of each layout. In each configuration shown in FIG. 12A to FIG. 12D, the oil supplied from the oil pump is supplied to the compression mechanism and the expansion mechanism via an oil supply passage provided in the shaft. That is, the oil passes through one of the compression mechanism and the expansion mechanism, and thereafter passes through the other. This causes the heat transfer to occur between the compression mechanism and the expansion mechanism via the oil.